Vacuum Use
For nozzles that are used in vacuum or at very high altitude, it is impossible to match ambient pressure; rather, larger area ratio nozzles are usually more efficient. However, a very long nozzle has significant mass, a drawback in and of itself. A length that optimises overall vehicle performance typically has to be found. Additionally, as the temperature of the gas in the nozzle decreases some components of the exhaust gases (such as water vapour from the combustion process) may condense, or even freeze. This is highly undesirable and needs to be avoided.
Magnetic nozzles have been proposed for some types of propulsion (for example VASIMR), in which the flow of plasma or ions are directed by magnetic fields instead of walls made of solid materials. These can be advantageous since a magnetic field itself cannot melt and the plasma temperatures can reach millions of kelvins. However, there are often thermal design challenges presented by the coils themselves, particularly if superconducting coils are used to form the throat and expansion fields.
Read more about this topic: Rocket Engine Nozzle
Famous quotes containing the word vacuum:
“No, it wasn’t an accident, I didn’t say that. It was carefully planned, down to the tiniest mechanical and emotional detail. But it was a mistake. It was a beaut. In the end, somehow granted the time for examination, we shall find that our so-called civilization was gloriously destroyed by a handful of vacuum tubes and transistors. Probably faulty.”
—John Paxton (1911–1985)
“If it were possible to have a life absolutely free from every feeling of sin, what a terrifying vacuum it would be!”
—Cesare Pavese (1908–1950)